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Monitoring the impact of climate change andhuman activities on grassland vegetation dynamics in the northeastern Qinghai-Tibet Plateauof China during 2000-2015
Qinli XIONG, Yang XIAO, Waseem A HALMY Marwa, A DAKHIL Mohammed, Pinghan LIANG, Chenggang LIU, Lin ZHANG, PANDEY Bikram, Kaiwen PAN, B EL KAFRAWAY Sameh, Jun CHEN
Journal of Arid Land    2019, 11 (5): 637-651.   DOI: 10.1007/s40333-019-0061-2
Abstract1016)   HTML48)    PDF(pc) (1276KB)(913)       Save

Climate change and human activities can influence vegetation net primary productivity (NPP), a key component of natural ecosystems. The Qinghai-Tibet Plateau of China, in spite of its significant natural and cultural values, is one of the most susceptible regions to climate change and human disturbancesin the world. To assess the impact of climate change and human activities on vegetation dynamics in the grassland ecosystems ofthe northeastern Qinghai-Tibet Plateau, we applied a time-series trend analysis to normalized difference vegetation index (NDVI) datasets from 2000 to 2015 and compared these spatiotemporal variations with trends in climatic variables over the same time period. The constrained ordination approach (redundancy analysis) was used to determine which climatic variables or human-related factors mostly in?uenced the variation of NDVI. Furthermore, in order to determine whether current conservation measures and programs are effectivein ecological protection and reconstruction, we divided the northeastern Qinghai-Tibet Plateau into two parts: the Three-River Headwater conservation area (TRH zone) in the south and the non-conservation area (NTRH zone) in the north. The results indicatedan overall (73.32%)increasing trend of vegetation NPP in grasslands throughout the study area. During the period 2000-2015, NDVI in the TRH and NTRH zones increased at the rates of 0.0015/aand 0.0020/a, respectively.Specifically, precipitation accounted for 9.2% of the total variation in NDVI, while temperature accounted for 13.4%. In addition, variation in vegetation NPP of grasslands responded not only to long- and short-term changes in climate, as conceptualized in non-equilibrium theory, but also to the impact of human activities and their associated perturbations. The redundancy analysis successfully separated the relative contributions of climate change and human activities, of whichvillage populationand agricultural gross domestic product were the two most important contributors to the NDVI changes, explaining 17.8% and 17.1% of the total variationof NDVI (with the total contribution >30.0%), respectively. The total contributionpercentages of climate change and human activitiesto the NDVI variation were27.5% and 34.9%, respectively, inthe northeastern Qinghai-Tibet Plateau. Finally, our study shows that the grassland restoration in the study area was enhanced by protection measures and programs in the TRH zone, which explained 7.6% of the total variation in NDVI.

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Responses of plant community to the linkages in plant-soil C:N:P stoichiometry during secondary succession of abandoned farmlands, China
LIU Weichao, FU Shuyue, YAN Shengji, REN Chengjie, WU Shaojun, DENG Jian, LI Boyong, HAN Xinhui, YANG Gaihe
Journal of Arid Land    2020, 12 (2): 215-226.   DOI: 10.1007/s40333-020-0009-6
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Succession is one of the central themes of ecology; however, the relationship between aboveground plant communities and underground soils during secondary succession remains unclear. In this study, we investigated the composition of plant community, plant-soil C:N:P stoichiometry and their relationships during secondary succession after the abandonment of farmlands for 0, 10, 20, 30, 40 and 50 a in China, 2016. Results showed that the composition of plant communities was most diverse in the farmlands after secondary succession for 20 and 50 a. Soil organic carbon and total nitrogen contents slightly decreased after secondary succession for 30 a, but both were significantly higher than those of control farmland (31.21%-139.10% and 24.24%-121.21%, respectively). Moreover, C:N ratios of soil and microbe greatly contributed to the changes in plant community composition during secondary succession of abandoned farmlands, explaining 35.70% of the total variation. Particularly, soil C:N ratio was significantly and positively related with the Shannon-Wiener index. This study provides the evidence of synchronous evolution between plant community and soil during secondary succession and C:N ratio is an important linkage between them.

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Factors determining soil water heterogeneity on the Chinese Loess Plateau as based on an empirical mode decomposition method
GONG Yidan, XING Xuguang, WANG Weihua
Journal of Arid Land    2020, 12 (3): 462-472.   DOI: 10.1007/s40333-020-0068-8
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Soil water is a critical resource, and as such is the focus of considerable physical research. Characterization of the distribution and spatial variability of soil water content (SWC) offers important agronomic and environmental information. Estimation of non-stationary and non-linear SWC distribution at different scales is a research challenge. Based on this context, we performed a case study on the Chinese Loess Plateau, with objectives of investigating spatial variability of SWC and soil properties (i.e., soil particle composition, organic matter and bulk density), and determining multi-scale correlations between SWC and soil properties. A total of 86 in situ sampling sites were selected and 516 soil samples (0-60 cm depth with an interval of 10 cm) were collected in May and June of 2019 along the Yangling-Wugong-Qianxian transect, with a length of 25.5 km, in a typical wheat-corn rotation region of the Chinese Loess Plateau. Classical statistics and empirical mode decomposition (EMD) method were applied to evaluate characteristics of the overall and scale-specific spatial variation of SWC, and to explore scale-specific correlations between SWC and soil properties. Results showed that the spatial variability of SWC along the Yangling-Wugong-Qianxian transect was medium to weak, with a variability coefficient range of 0.06-0.18, and it was gradually decreased as scale increased. We categorized the overall SWC for each soil layer under an intrinsic mode function (IMF) number based on the scale of occurrence, and found that the component IMF1 exhibited the largest contribution rates of 36.45%-56.70%. Additionally, by using EMD method, we categorized the general variation of SWC under different numbers of IMFs according to occurrence scale, and the results showed that the calculated scales among SWC for each soil layer increased in correspondence with higher IMF numbers. Approximately 78.00% of the total variance of SWC was extracted in IMF1 and IMF2. Generally, soil texture was the dominant control on SWC, and the influence of the three types of soil properties (soil particle composition, organic matter and bulk density) was more prominent at larger scales along the sampling transect. The influential factors of soil water spatial distribution can be identified and ranked on the basis of the decomposed signal from the current approach, thereby providing critical information for other researchers and natural resource managers.

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Environmental factors influencing snowfall and snowfall prediction in the Tianshan Mountains, Northwest China
Xueting ZHANG, Xuemei LI, Lanhai LI, Shan ZHANG, Qirui QIN
Journal of Arid Land    2019, 11 (1): 15-28.   DOI: 10.1007/s40333-018-0110-2
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Snowfall is one of the dominant water resources in the mountainous regions and is closely related to the development of the local ecosystem and economy. Snowfall predication plays a critical role in understanding hydrological processes and forecasting natural disasters in the Tianshan Mountains, where meteorological stations are limited. Based on climatic, geographical and topographic variables at 27 meteorological stations during the cold season (October to April) from 1980 to 2015 in the Tianshan Mountains located in Xinjiang of Northwest China, we explored the potential influence of these variables on snowfall and predicted snowfall using two methods: multiple linear regression (MLR) model (a conventional measuring method) and random forest (RF) model (a non-parametric and non-linear machine learning algorithm). We identified the primary influencing factors of snowfall by ranking the importance of eight selected predictor variables based on the relative contribution of each variable in the two models. Model simulations were compared using different performance indices and the results showed that the RF model performed better than the MLR model, with a much higher R2 value (R2=0.74; R2, coefficient of determination) and a lower bias error (RSR=0.51; RSR, the ratio of root mean square error to standard deviation of observed dataset). This indicates that the non-linear trend is more applicable for explaining the relationship between the selected predictor variables and snowfall. Relative humidity, temperature and longitude were identified as three of the most important variables influencing snowfall and snowfall prediction in both models, while elevation, aspect and latitude were of secondary importance, followed by slope and wind speed. These results will be beneficial to understand hydrological modeling and improve management and prediction of water resources in the Tianshan Mountains.

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Arbuscular mycorrhizal fungi ameliorate the chemical properties and enzyme activities of rhizosphere soil in reclaimed mining subsidence in northwestern China
Lang QIU, Yinli BI, Bin JIANG, Zhigang WANG, Yanxu ZHANG, ZHAKYPBEK Yryszhan
Journal of Arid Land    2019, 11 (1): 135-147.   DOI: 10.1007/s40333-018-0019-9
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In semi-arid region of northwestern China, underground mining subsidence often results in decreased vegetation coverage, impoverishment of soil fertility and water stress. In addition, the physical-chemical and biological properties of soil also change, resulting in more susceptible to degradation. In particular, subsidence causes disturbance of the symbioses of plant and microbe that can play a beneficial role in the establishment of vegetation communities in degraded ecosystems. The objective of this study was to evaluate the effects of revegetation with exotic arbuscular mycorrhizal fungi (AMF) inoculum on the chemical and biological properties of soil over time in mining subsidence areas. Soils were sampled at a depth up to 30 cm in the adjacent rhizosphere of Amorpha fruticose Linn. from five reclaimed vegetation communities in northwestern China. In August 2015, a field trial was set up with five historical revegetation experiments established in 2008 (7-year), 2011 (4-year), 2012 (3-year), 2013 (2-year) and 2014 (1-year), respectively. Each reclamation experiment included two treatments, i.e., revegetation with exotic AMF inoculum (AMF) and non-AMF inoculum (the control). Root mycorrhizal colonization, glomalin-related soil protein (GRSP), soil organic carbon (SOC), soil nutrients, and enzyme activities were also assessed. The results showed that mycorrhizal colonization of inoculated plants increased by 33.3%-163.0% compared to that of non-inoculated plants (P<0.05). Revegetation with exotic AMF inoculum also significantly improved total GRSR (T-GRSP) and easily extracted GRSP (EE-GRSP) concentrations compared to control, besides the T-GRSP in 1-year experiment and the EE-GRSP in 2-year experiment. A significant increase in SOC content was only observed in 7-year AMF reclaimed soils compared to non-AMF reclaimed soils. Soil total N (TN), Olsen phosphorus (P) and available potassium (K) were significantly higher in inoculated soil after 1-7 years of reclamation (except for individual cases), and increased with reclamation time (besides soil Olsen P). The exotic AMF inoculum markedly increased the average soil invertase, catalase, urease and alkaline phosphatase by 23.8%, 21.3%, 18.8% and 8.6%, respectively (P<0.01), compared with the control. Root mycorrhizal colonization was positively correlated with soil parameters (SOC, TN and soil available K) and soil enzyme activities (soil invertase, catalase, urease and alkaline phosphatase) in both AMF and non-AMF reclaimed soils (P<0.05), excluding available K in non-AMF reclaimed soils. T-GRSP (P<0.01) and EE-GRSP (P<0.05) were significantly correlated with the majority of edaphic factors, except for soil Olsen P. The positive correlation between root mycorrhizal colonization and available K was observed in AMF reclaimed soils, indicating that the AMF reclaimed soil with a high root mycorrhizal colonization could potentially accumulate available K in soils. Our findings concluded that revegetation with exotic AMF inoculum influenced soil nutrient availability and enzyme activities in the semi-arid ecosystem, suggesting that inoculating AMF can be an effective method to improve soil fertility and support restoration of vegetation communities under poor conditions like soil nutrient deficiency and drought.

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Hydrological and economic feasibility of mitigating a stressed coastal aquifer using managed aquifer recharge: a case study of Jamma aquifer, Oman
EL-RAWY Mustafa, AL-MAKTOUMI Ali, ZEKRI Slim, ABDALLA Osman, AL-ABRI Rashid
Journal of Arid Land    2019, 11 (1): 148-159.   DOI: 10.1007/s40333-019-0093-7
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This study explored the hydrological and economic feasibility of managed aquifer recharge (MAR) using tertiary treated wastewater (TWW) to mitigate salinity in the coastal aquifer of Jamma, Oman. A steady-state groundwater flow and transport model, using MODFLOW software, was developed and calibrated. Different managerial scenarios were simulated and the results reveal that the Jamma aquifer will be further deteriorated in the next 20 a if it remains unmanaged. The groundwater table will decline further by more than 3 m on average; and the iso-concentration salinity line of 1500 mg/L will advance 2.7 km inland, which will severely affect the farming activities in the area. However, MAR using TWW when integrated with the management of groundwater abstraction (e.g., using modern irrigation systems to reduce the abstraction rate) becomes hydrologically feasible to augment the aquifer storage and control seawater intrusion, and hence improves the farming activities. The results indicate that: (1) injecting TWW in the vicinity of irrigation wells (Scenario A2); (2) investing in smart water meters and online control of pumping from the wells to reduce the abstraction rate by 25% (Scenario B); and (3) a combination of both (Scenario B2) are feasible scenarios with positive net present values. Recharge in upstream areas is found not economically feasible because of the very high investment cost of the installation of pipes to transport the TWW over a distance of 12.5 km. Because of securing funds are challenging, Scenario B would be the best option and the second-best option is Scenario A2. Scenario B2 has the lowest net benefit investment ratio and is very attractive because it entails integrated demand and supply management of groundwater. It is required to reduce pumping and to invest in injecting TWW to improve groundwater quality in the vicinity of irrigation wells and to form a hydrological barrier to control seawater intrusion in the long run.

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Prediction of meteorological drought in arid and semi-arid regions using PDSI and SDSM: a case study in Fars Province, Iran
Sheida DEHGHAN, Nasrin SALEHNIA, Nasrin SAYARI, Bahram BAKHTIARI
Journal of Arid Land    2020, 12 (2): 318-330.   DOI: 10.1007/s40333-020-0095-5
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Drought is one of the most significant environmental disasters, especially in arid and semi-arid regions. Drought indices as a tool for management practices seeking to deal with the drought phenomenon are widely used around the world. One of these indicators is the Palmer drought severity index (PDSI), which is used in many parts of the world to assess the drought situation and continuation. In this study, the drought state of Fars Province in Iran was evaluated by using the PDSI over 1995-2014 according to meteorological data from six weather stations in the province. A statistical downscaling model (SDSM) was used to apply the output results of the general circulation model in Fars Province. To implement data processing and prediction of climate data, a statistical period 1995-2014 was considered as the monitoring period, and a statistical period 2019-2048 was for the prediction period. The results revealed that there is a good agreement between the simulated precipitation (R2>0.63; R2, determination coefficient; MAE<0.52; MAE, mean absolute error; RMSE<0.56; RMSE, Root Mean Squared Error) and temperature (R2>0.95, MAE<1.74, and RMSE<1.78) with the observed data from the stations. The results of the drought monitoring model presented that dry periods would increase over the next three decades as compared to the historical data. The studies showed the highest drought in the meteorological stations Abadeh and Lar during the prediction period under two future scenarios representative concentration pathways (RCP4.5 and RCP8.5). According to the results of the validation periods and efficiency criteria, we suggest that the SDSM is a proper tool for predicting drought in arid and semi-arid regions.

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Climate change, water resources and sustainable development in the arid and semi-arid lands of Central Asia in the past 30 years
Yang YU, Yuanyue PI, Xiang YU, Zhijie TA, Lingxiao SUN, DISSE Markus, Fanjiang ZENG, Yaoming LI, Xi CHEN, Ruide YU
Journal of Arid Land    2019, 11 (1): 1-14.   DOI: 10.1007/s40333-018-0073-3
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The countries of Central Asia are collectively known as the five ''-stans'': Uzbekistan, Kyrgyzstan, Turkmenistan, Tajikistan and Kazakhstan. In recent times, the Central Asian region has been affected by the shrinkage of the Aral Sea, widespread desertification, soil salinization, biodiversity loss, frequent sand storms, and many other ecological disasters. This paper is a review article based upon the collection, identification and collation of previous studies of environmental changes and regional developments in Central Asia in the past 30 years. Most recent studies have reached a consensus that the temperature rise in Central Asia is occurring faster than the global average. This warming trend will not only result in a higher evaporation in the basin oases, but also to a significant retreat of glaciers in the mountainous areas. Water is the key to sustainable development in the arid and semi-arid regions in Central Asia. The uneven distribution, over consumption, and pollution of water resources in Central Asia have caused severe water supply problems, which have been affecting regional harmony and development for the past 30 years. The widespread and significant land use changes in the 1990s could be used to improve our understanding of natural variability and human interaction in the region. There has been a positive trend of trans-border cooperation among the Central Asian countries in recent years. International attention has grown and research projects have been initiated to provide water and ecosystem protection in Central Asia. However, the agreements that have been reached might not be able to deliver practical action in time to prevent severe ecological disasters. Water management should be based on hydrographic borders and ministries should be able to make timely decisions without political intervention. Fully integrated management of water resources, land use and industrial development is essential in Central Asia. The ecological crisis should provide sufficient motivation to reach a consensus on unified water management throughout the region.

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Changes in soil microbial community response to precipitation events in a semi-arid steppe of the Xilin River Basin, China
Hui ZHANG, Wenjun LIU, Xiaoming KANG, Xiaoyong CUI, Yanfen WANG, Haitao ZHAO, Xiaoqing QIAN, Yanbin HAO
Journal of Arid Land    2019, 11 (1): 97-110.   DOI: 10.1007/s40333-018-0071-5
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In the context of climate change, precipitation is predicted to become more intense at the global scale. Such change may alter soil microbial communities and the microbially mediated carbon and nitrogen dynamics. In this study, we experimentally repackaged precipitation patterns during the growing season (from June to September) of 2012 in a semi-arid temperate steppe of the Xilin River Basin in Inner Mongolia of China, based on the 60-year growing season precipitation data. Specifically, a total amount of 240 mm simulated precipitation was assigned to experimental plots by taking the following treatments: (1) P6 (6 extreme precipitation events, near the 1st percentile); (2) P10 (10 extreme precipitation events, near the 5th percentile); (3) P16 (16 moderate precipitation events, near the 50th percentile); and (4) P24 (24 events, 60-year average precipitation, near the 50th percentile). At the end of the growing season, we analyzed soil microbial community structure and biomass, bacterial abundance, fungal abundance and bacterial composition, by using phospholipid fatty acid (PLFA), real-time quantitative polymerase chain reaction (RT-qPCR) and 16S rRNA gene clone library methods. The extreme precipitation events did not change soil microbial community structure (represented by the ratio of PLFA concentration in fungi to PLFA concentration in bacteria, and the ratio of PLFA concentration in gram-positive bacterial biomass to PLFA concentration in gram-negative bacterial biomass). However, the extreme precipitation events significantly increased soil microbial activity (represented by soil microbial biomass nitrogen and soil bacterial 16S rRNA gene copy numbers). Soil fungal community showed no significant response to precipitation events. According to the redundancy analysis, both soil microbial biomass nitrogen and soil ammonium nitrogen (NH4-N) were found to be significant in shaping soil microbial community. Acidobacteria, Actinobacteria and Proteobacteria were the dominant phyla in soil bacterial composition, and responded differently to the extreme precipitation events. Based on the results, we concluded that the extreme precipitation events altered the overall soil microbial activity, but did not impact how the processes would occur, since soil microbial community structure remained unchanged.

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Spatial and temporal change patterns of net primary productivity and its response to climate change in the Qinghai-Tibet Plateau of China from 2000 to 2015
GUO Bing, ZANG Wenqian, YANG Fei, HAN Baomin, CHEN Shuting, LIU Yue, YANG Xiao, HE Tianli, CHEN Xi, LIU Chunting, GONG Rui
Journal of Arid Land    2020, 12 (1): 1-17.   DOI: 10.1007/s40333-019-0070-1
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The vegetation ecosystem of the Qinghai-Tibet Plateau in China, considered to be the ′′natural laboratory′′ of climate change in the world, has undergone profound changes under the stress of global change. Herein, we analyzed and discussed the spatial-temporal change patterns and the driving mechanisms of net primary productivity (NPP) in the Qinghai-Tibet Plateau from 2000 to 2015 based on the gravity center and correlation coefficient models. Subsequently, we quantitatively distinguished the relative effects of climate change (such as precipitation, temperature and evapotranspiration) and human activities (such as grazing and ecological construction) on the NPP changes using scenario analysis and Miami model based on the MOD17A3 and meteorological data. The average annual NPP in the Qinghai-Tibet Plateau showed a decreasing trend from the southeast to the northwest during 2000-2015. With respect to the inter-annual changes, the average annual NPP exhibited a fluctuating upward trend from 2000 to 2015, with a steep increase observed in 2005 and a high fluctuation observed from 2005 to 2015. In the Qinghai-Tibet Plateau, the regions with the increase in NPP (change rate higher than 10%) were mainly concentrated in the Three-River Source Region, the northern Hengduan Mountains, the middle and lower reaches of the Yarlung Zangbo River, and the eastern parts of the North Tibet Plateau, whereas the regions with the decrease in NPP (change rate lower than -10%) were mainly concentrated in the upper reaches of the Yarlung Zangbo River and the Ali Plateau. The gravity center of NPP in the Qinghai-Tibet Plateau has moved southwestward during 2000-2015, indicating that the increment and growth rate of NPP in the southwestern part is greater than those of NPP in the northeastern part. Further, a significant correlation was observed between NPP and climate factors in the Qinghai-Tibet Plateau. The regions exhibiting a significant correlation between NPP and precipitation were mainly located in the central and eastern Qinghai-Tibet Plateau, and the regions exhibiting a significant correlation between NPP and temperature were mainly located in the southern and eastern Qinghai-Tibet Plateau. Furthermore, the relative effects of climate change and human activities on the NPP changes in the Qinghai-Tibet Plateau exhibited significant spatial differences in three types of zones, i.e., the climate change-dominant zone, the human activity-dominant zone, and the climate change and human activity interaction zone. These research results can provide theoretical and methodological supports to reveal the driving mechanisms of the regional ecosystems to the global change in the Qinghai-Tibet Plateau.

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Spatial and temporal patterns of drought in Zambia
LIBANDA Brigadier, Mie ZHENG, NGONGA Chilekana
Journal of Arid Land    2019, 11 (2): 180-191.   DOI: 10.1007/s40333-019-0053-2
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Drought acutely affects economic sectors, natural habitats and communities. Understanding the past spatial and temporal patterns of drought is crucial because it facilitates the forecasting of future drought occurrences and informs decision-making processes for possible adaptive measures. This is especially important in view of a changing climate. This study employed the World Meteorological Organization (WMO)-recommended standardized precipitation index (SPI) to investigate the spatial and temporal patterns of drought in Zambia from 1960 to 2016. The relationship between the occurrence of consecutive dry days (CDD; consecutive days with less than 1 mm of precipitation) and SPI was also investigated. Horizontal wind vectors at 850 hPa during the core of the rainy season (December-February) were examined to ascertain the patterns of flow during years of extreme and severe drought; and these were contrasted with the patterns of flow in 2007, which was a generally wet year. Pressure vertical velocity was also investigated. Based on the gamma distribution, SPI successfully categorized extremely dry (with a SPI value less than or equal to -2.0) years over Zambia as 1992 and 2015, a severely dry (-1.9 to -1.5) year as 1995, moderately dry (-1.4 to -1.0) years as 1972, 1980, 1987, 1999 and 2005, and 26 near normal years (-0.9 to 0.9). The occurrence of CDD was found to be strongly negatively correlated with SPI with a coefficient of -0.6. Further results suggest that, during wet years, Zambia is influenced by a clockwise circulating low-pressure zone over the south-eastern Angola, a second such zone over the northern and eastern parts, and a third over the Indian Ocean. In stark contrast, years of drought were characterized by an anti-clockwise circulating high-pressure zone over the south-western parts of Zambia, constraining precipitation activities over the country. Further, wet years were characterized by negative pressure vertical velocity anomalies, signifying ascending motion; while drought years were dominated by positive anomalies, signifying descending motion, which suppresses precipitation. These patterns can be used to forecast drought over Zambia and aid in strategic planning to limit the potential damage of drought.

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Coupling analysis of social-economic water consumption and its effects on the arid environments in Xinjiang of China based on the water and ecological footprints
ZHANG Pei, DENG Mingjiang, LONG Aihua, DENG Xiaoya, WANG Hao, HAI Yang, WANG Jie, LIU Yundong
Journal of Arid Land    2020, 12 (1): 73-89.   DOI: 10.1007/s40333-020-0050-5
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In arid areas, ecological degradation aroused by over-exploitation of fresh water, expansion of artificial oasis and shrinkage of natural oasis, has drawn attention of many scholars and officials. The water and ecological footprints can be used to quantitatively evaluate the water consumption of social-economic activities and their influence on the eco-environments. In addition, increase of the water footprint indicates the expansion of artificial oasis, and the influence on the natural oasis could be reflected by the variation of the ecological footprint. This study was conducted to answer a scientific question that what is the quantitative relationship between the expansion of the artificial oasis and the degradation of the natural oasis in the arid environments of Xinjiang, China. Thus, based on the social-economic data, water consumption data and meteorological data during 2001-2015, we calculated the water and ecological footprints to express the human-related pressure exerted on the water resources and arid environments in Xinjiang (including 14 prefectures and cities), and explore the relationship between the water and ecological footprints and its mechanism by using the coupling analysis and Granger causality test. The results show that both the water and ecological footprints of Xinjiang increased significantly during 2001-2015, and the increasing rate of the ecological footprint was much faster than that of the water footprint. The coupling degree between the water and ecological footprints was relatively high at the temporal scale and varied at the spatial scale. Among the 14 prefectures and cities examined in Xinjiang, the greater social-economic development (such as in Karamay and Urumqi) was associated with the lower coupling degree between the two footprints. Increases in the water footprint will cause the ecological footprint to increase, such that a 1-unit increase in the consumption of water resources would lead to 2-3 units of ecological degradation. The quantitative relationship between the increases of the water and ecological footprints, together with the intensities of water consumption both in the natural and artificial oases of Tarim River Basin, have approved the fact that the formation and expansion of 1 unit of the artificial oasis would bring about the degradation of 2 units of the natural oasis. These conclusions not only provide a technical basis for sustainable development in Xinjiang, but also offer a theoretical guide and scientific information that could be used in similar arid areas around the world.

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Development of a large-scale remote sensing ecological index in arid areas and its application in the Aral Sea Basin
WANG Jie, LIU Dongwei, MA Jiali, CHENG Yingnan, WANG Lixin
Journal of Arid Land    2021, 13 (1): 40-55.   DOI: 10.1007/s40333-021-0052-y
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The Aral Sea Basin in Central Asia is an important geographical environment unit in the center of Eurasia. It is of great significance to the ecological protection and sustainable development of Central Asia to carry out dynamic monitoring and effective evaluation of the eco-environmental quality of the Aral Sea Basin. In this study, the arid remote sensing ecological index (ARSEI) for large-scale arid areas was developed, which coupled the information of the greenness index, the salinity index, the humidity index, the heat index, and the land degradation index of arid areas. The ARSEI was used to monitor and evaluate the eco-environmental quality of the Aral Sea Basin from 2000 to 2019. The results show that the greenness index, the humidity index and the land degradation index had a positive impact on the quality of the ecological environment in the Aral Sea Basin, while the salinity index and the heat index exerted a negative impact on the quality of the ecological environment. The eco-environmental quality of the Aral Sea Basin demonstrated a trend of initial improvement, followed by deterioration, and finally further improvement. The spatial variation of these changes was significant. From 2000 to 2019, grassland and wasteland (saline alkali land and sandy land) in the central and western parts of the basin had the worst ecological environment quality. The areas with poor ecological environment quality are mainly distributed in rivers, wetlands, and cultivated land around lakes. During the period from 2000 to 2019, except for the surrounding areas of the Aral Sea, the ecological environment quality in other areas of the Aral Sea Basin has been improved in general. The correlation coefficients between the change in the eco-environmental quality and the heat index and between the change in the eco-environmental quality and the humidity index were -0.593 and 0.524, respectively. Climate conditions and human activities have led to different combinations of heat and humidity changes in the eco-environmental quality of the Aral Sea Basin. However, human activities had a greater impact. The ARSEI can quantitatively and intuitively reflect the scale and causes of large-scale and long-time period changes of the eco-environmental quality in arid areas; it is very suitable for the study of the eco-environmental quality in arid areas.

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Assessment of desertification in Eritrea: land degradation based on Landsat images
G GHEBREZGABHER Mihretab, Taibao YANG, Xuemei YANG, Congqiang WANG
Journal of Arid Land    2019, 11 (3): 319-331.   DOI: 10.1007/s40333-019-0096-4
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Remote sensing is an effective way in monitoring desertification dynamics in arid and semi-arid regions. In this study, we used a decision tree method based on NDVI (normalized difference vegetation index), SAVI (soil adjusted vegetation index), and vegetation cover proportion to quantify and analyze the desertification in Eritrea using Landsat data of the 1970s, 1980s and 2014. The results demonstrate that the NDVI value and the annual mean precipitation declined while the temperature increased over the past 40 a. Strongly desertified land increased from 4.82×104 km2 (38.5%) in the 1970s to 8.38×104 km2(66.9%) in 2014: approximately 85% of the land of the countrywas under serious desertification, which significantly occurred in arid and semi-arid lowlands of the country (eastern, northern, and western lowlands)withrelatively scarce precipitation and high temperature. The non-desertified area, mostly located in the sub-humid eastern escarpment, also declined from approximately 2.1% to 0.5%. The study concludes that the desertification is a cause of serious land degradation in Eritrea and may link to climate changes, such as low and unpredictable precipitation, and prolonged drought.

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Interaction between climate and management on beta diversity components of vegetation in relation to soil properties in arid and semi-arid oak forests, Iran
MEHDI Heydari, FATEMEH Aazami, MARZBAN Faramarzi, REZA Omidipour, MASOUD Bazgir, DAVID Pothier, BERNARD Prévosto
Journal of Arid Land    2019, 11 (1): 43-57.   DOI: 10.1007/s40333-018-0024-z
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This study aimed to investigate the interaction between regions with different climatic conditions (arid vs. semi-arid) and management (protected vs. unprotected) on the turnover and nestedness of vegetation in relation to physical, chemical and biological properties of soils in the Ilam Province of Iran. In each of the two regions, we sampled 8 sites (4 managed and 4 unmanaged sites) within each of which we established 4 circular plots (1000 m2) that were used to investigate woody species, while two micro-plots (1 m×1 m) were established in each 1000-m2 plot to analyze herbaceous species. In each sample unit, we also extracted three soil samples (0-20 cm depth) for measuring soil properties. The results indicated that the interaction between region and conservational management significantly affected the percent of canopy cover of Persian oak (Quercus brantii Linddl), soil respiration, substrate-induced respiration, as well as beta and gamma diversities and turnover of plant species. The percent of oak canopy cover was positively correlated with soil silt, electrical conductivity, available potassium, and alpha diversity, whereas it was negatively correlated with plant turnover. In addition, plant turnover was positively related to available phosphorus, while nestedness of species was positively related to organic carbon and total nitrogen. According to these results, we concluded that physical, chemical, and biological characteristics of limited ecological niche generally influenced plant diversity. Also, this study demonstrated the major contribution of the beta diversity on gamma diversity, especially in semi-arid region, because of the higher heterogeneity of vegetation in this area.

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Seasonal changes in the water-use strategies of three herbaceous species in a native desert steppe of Ningxia, China
HU Haiying, ZHU Lin, LI Huixia, XU Dongmei, XIE Yingzhong
Journal of Arid Land    2021, 13 (2): 109-122.   DOI: 10.1007/s40333-021-0051-z
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Frequent periods of drought conditions are known to limit plant performance, primary production, and ecosystem stability in arid and semi-arid desert steppe environments. Plants often avoid competition by shifting their water use seasonally, which affects the water-use patterns of dominant species as well as the composition and structure of plant communities. However, the water-use strategies of dominant herbaceous species, which grow under natural field conditions in the desert steppe region of Ningxia Hui Autonomous Region, China, are poorly known. Here, we explored the possible sources of water uptake and water-use efficiency (WUE) of three dominant herbaceous plant species (Stipa breviflora, Agropyron mongolicum, and Glycyrrhiza uralensis) in a native desert steppe in the semi-arid area of Ningxia through an analysis of multiple parameters, including (1) the stable isotopic oxygen and hydrogen (δ 18O and δ 2H) compositions of precipitation, soil water, and stem water, (2) the carbon isotope ( 13C) composition of leaves, and (3) the soil water contents, based on field sampling across varying water conditions from June to September, 2017. Frequent small precipitation events replenished shallow soil water, whereas large events only percolated down to the deep soil layers. Changes in soil water availability affected the water-use patterns of plants. Generally, during light precipitation periods, the deep root system of G. uralensis accessed deeper (>80 cm) soil water, whereas S. breviflora and A. mongolicum, which only have shallow roots, primarily absorbed water from the shallow and middle soil layers. As precipitation increased, all three plant species primarily obtained water from the shallow soil layers. Variation in soil water uptake between the dry and wet seasons enabled plants to make better use of existing satoil water. In addition, the δ 13C values of G. uralensis and S. breviflora were higher than those of A. mongolicum. The δ 13C values of the three plant species were significantly negatively correlated with soil water content. Therefore, G. uralensis and S. breviflora maintained a higher WUE through their conservative and water-saving strategies across the entire growing season. In contrast, A. mongolicum, with a relatively low WUE in the wet season but a high WUE in the dry season, exhibited a more flexible water-use strategy. The different water-use strategies of these dominant plant species demonstrated the mechanisms by which plant communities can respond to drought.

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Rehabilitation of degraded areas in northeastern Patagonia, Argentina: Effects of environmental conditions and plant functional traits on performance of native woody species
Juan M ZEBERIO, Carolina A PéREZ
Journal of Arid Land    2020, 12 (4): 653-665.   DOI: 10.1007/s40333-020-0021-x
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Degradation processes affect a vast area of arid and semi-arid lands around the world and damage the environment and people′s health. Degradation processes are driven by human productive activities that cause direct and indirect effects on natural resources, such as species extinction at regional scale, reduction and elimination of vegetation cover, soil erosion, etc. In this context, ecological rehabilitation is an important tool to recover key aspects of the degraded ecosystem. Rehabilitation trials rely on the use of native plant species with characteristics that allow them to obtain high survival and growth rates. The aim of this work was to assess the survival and growth of native woody species in degraded areas of northeastern Patagonia and relate them to plant functional traits and environmental variables. We observed high early and late survival rates, and growth rates in Prosopis flexuosa DC. var. depressa F.A. Roig and Schinus johnstonii F.A. Barkley, and low values in Condalia microphylla Cav. and Geoffroea decorticans (Gillies ex Hook. & Arn.) Burkart. Early survival rates were positively associated with specific leaf area (SLA) and precipitation, but negatively associated with wood density, the maximum mean temperature of the warmest month and the minimum mean temperature of the coldest month. Late survival rates were positively associated with SLA and soil organic matter, but negatively associated with plant height and precipitation. The temperature had a positive effect on late survival rates once the plants overcame the critical period of the first summer after they were transplanted to the field. Prosopis flexuosa and S. johnstonii were the most successful species in our study. This could be due to their functional traits that allow these species to acclimatize to the local environment. Further research should focus on C. microphylla and G. decorticans to determine how they relate to productive conditions, acclimation to environmental stress, auto-ecology and potential use in ecological rehabilitation trials.

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Water transport and water use efficiency differ among Populus euphratica Oliv. saplings exposed to saline water irrigation
ZHOU Honghua, CHEN Yaning, ZHU Chenggang, YANG Yuhai, YE Zhaoxia
Journal of Arid Land    2019, 11 (6): 866-879.   DOI: 10.1007/s40333-019-0002-0
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Populus euphratica Oliv. is a unique woody tree that can be utilized for vegetation restoration in arid and semi-arid areas. The effects of saline water irrigation (0.00, 2.93, 8.78 and 17.55 g/L NaCl solutions) on water transport and water use efficiency (WUE) of P. euphratica saplings were researched for improving the survival of P. euphratica saplings and vegetation restoration in arid and semi-arid areas of Xinjiang, China in 2011. Results showed that hydraulic conductivity and vulnerability to cavitation of P. euphratica saplings were more sensitive in root xylem than in twig xylem when irrigation water salinity increased. Irrigation with saline water concentration less than 8.78 g/L did not affect the growth of P. euphratica saplings, under which they maintained normal water transport in twig xylem through adjustment of anatomical structure of vessels and kept higher WUE and photosynthesis in leaves through adjustment of stomata. However, irrigation with saline water concentration up to 17.55 g/L severely inhibited the photochemical process and WUE of P. euphratica saplings, resulting in severe water-deficit in leaves and a sharp reduction in water transport in xylem. Thus, it is feasible to irrigate P. euphratica forest by using saline groundwater for improving the survival of P. euphratica saplings and vegetation restoration in arid and semi-arid areas of Xinjiang, China.

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Estimation of spatial and temporal changes in net primary production based on Carnegie Ames Stanford Approach (CASA) model in semi-arid rangelands of SemiromCounty, Iran
HADIAN Fatemeh, JAFARI Reza, BASHARI Hossein, TARTESH Mostafa, D CLARKE Kenneth
Journal of Arid Land    2019, 11 (4): 477-494.   DOI: 10.1007/s40333-019-0060-3
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Net primary production (NPP) is an indicator of rangeland ecosystem function. This research assessed the potential of the Carnegie Ames Stanford Approach (CASA) model for estimating NPP and its spatial and temporal changes in semi-arid rangelands of Semirom County, Iran. Using CASA model, we estimated the NPP values based on monthly climate data and the normalized difference vegetation index (NDVI) obtained from the MODIS sensor. Regression analysis was then applied to compare the estimated production data with observed production data. The spatial and temporal changes in NPP and light utilization efficiency (LUE) were investigated in different rangeland vegetation types. The standardized precipitation index (SPI) was also calculated at different time scales and the correlation of SPI with NPP changes was determined. The results indicated that the estimated NPP values varied from 0.00 to 74.48 g C/(m2?a). The observed and estimated NPP values had different correlations, depending on rangeland conditions and vegetation types. The highest and lowest correlations were respectively observed in Astragalus spp.-Agropyronspp. rangeland (R2=0.75) with good condition and Gundeliaspp.-Cousiniaspp. rangeland (R2=0.36) with poor and very poor conditions. The maximum and minimum LUE values were found in Astragalus spp.-Agropyronspp. rangeland (0.117 g C/MJ) with good condition and annual grasses-annual forbs rangeland (0.010 g C/MJ), respectively. According to the correlations between SPI and NPP changes, the effects of drought periods on NPP depended on vegetation types and rangeland conditions. Annual plants had the highest drought sensitivity while shrubs exhibited the lowest drought sensitivity. The positive effects of wet periods on NPP were less evident in degraded areas where the destructive effects of drought were more prominent. Therefore, determining vegetation types and rangeland conditions is essential in NPP estimation. The findings of this study confirmed the potential of the CASA for estimating rangeland production. Therefore, the model output maps can be used to evaluate, monitor and optimize rangeland management in semi-arid rangelands of Iran where MODIS NPP products are not available.

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Phenotypic plasticity of Artemisia ordosica seedlings in response to different levels of calcium carbonate in soil
Pingping XUE, Xuelai ZHAO, Yubao GAO, Xingdong HE
Journal of Arid Land    2019, 11 (1): 58-65.   DOI: 10.1007/s40333-018-0072-4
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Plant phenotypic plasticity is a common feature that is crucial for explaining interspecific competition, dynamics and biological evolution of plant communities. In this study, we tested the effects of soil CaCO3 (calcium carbonate) on the phenotypic plasticity of a psammophyte, Artemisia ordosica, an important plant species on sandy lands in arid and semi-arid areas of China, by performing pot experiments under different CaCO3 contents with a two-factor randomized block design and two orthogonal designs. We analyzed the growth responses (including plant height, root length, shoot-leaf biomass and root biomass) of A. ordosica seedlings to different soil CaCO3 contents. The results revealed that, with a greater soil CaCO3 content, A. ordosica seedlings gradually grew more slowly, with their relative growth rates of plant height, root length, shoot-leaf biomass and root biomass all decreasing significantly. Root N/P ratios showed significant negative correlations with the relative growth rates of plant height, shoot-leaf biomass and root length of A. ordosica seedlings; however, the relative growth rate of root length increased significantly with the root P concentration increased, showing a positive correlation. These results demonstrate that soil CaCO3 reduces the local P availability in soil, which produces a non-adaptive phenotypic plasticity to A. ordosica seedlings. This study should prove useful for planning and promoting the restoration of damaged/degraded vegetation in arid and semi-arid areas of China.

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Assessing the effects of vegetation and precipitation on soil erosion in the Three-River Headwaters Region of the Qinghai-Tibet Plateau, China
HE Qian, DAI Xiao'ai, CHEN Shiqi
Journal of Arid Land    2020, 12 (5): 865-886.   DOI: 10.1007/s40333-020-0075-9
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Soil erosion in the Three-River Headwaters Region (TRHR) of the Qinghai-Tibet Plateau in China has a significant impact on local economic development and ecological environment. Vegetation and precipitation are considered to be the main factors for the variation in soil erosion. However, it is a big challenge to analyze the impacts of precipitation and vegetation respectively as well as their combined effects on soil erosion from the pixel scale. To assess the influences of vegetation and precipitation on the variation of soil erosion from 2005 to 2015, we employed the Revised Universal Soil Loss Equation (RUSLE) model to evaluate soil erosion in the TRHR, and then developed a method using the Logarithmic Mean Divisia Index model (LMDI) which can exponentially decompose the influencing factors, to calculate the contribution values of the vegetation cover factor (C factor) and the rainfall erosivity factor (R factor) to the variation of soil erosion from the pixel scale. In general, soil erosion in the TRHR was alleviated from 2005 to 2015, of which about 54.95% of the area where soil erosion decreased was caused by the combined effects of the C factor and the R factor, and 41.31% was caused by the change in the R factor. There were relatively few areas with increased soil erosion modulus, of which 64.10% of the area where soil erosion increased was caused by the change in the C factor, and 23.88% was caused by the combined effects of the C factor and the R factor. Therefore, the combined effects of the C factor and the R factor were regarded as the main driving force for the decrease of soil erosion, while the C factor was the dominant factor for the increase of soil erosion. The area with decreased soil erosion caused by the C factor (12.10×103 km2) was larger than the area with increased soil erosion caused by the C factor (8.30×103 km2), which indicated that vegetation had a positive effect on soil erosion. This study generally put forward a new method for quantitative assessment of the impacts of the influencing factors on soil erosion, and also provided a scientific basis for the regional control of soil erosion.

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Relationship of species diversity between overstory trees and understory herbs along the environmental gradients in the Tianshan Wild Fruit Forests, Northwest China
CHENG Junhui, SHI Xiaojun, FAN Pengrui, ZHOU Xiaobing, SHENG Jiandong, ZHANG Yuanming
Journal of Arid Land    2020, 12 (4): 618-629.   DOI: 10.1007/s40333-020-0055-0
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In forest ecosystems, interactions between overstory trees and understory herbs play an important role in driving plant species diversity. However, reported links between overstory tree and understory herb species diversity have been inconsistent, due to variations in forest types and environmental conditions. Here, we measured species richness (SR) and diversity (Shannon-Wiener (H') and Simpson's (D) indices) of overstory trees and understory herbs in the protected Tianshan Wild Fruit Forest (TWFF), Northwest China, to explore their relationships along the latitudinal, longitudinal, elevational, and climatic (current climate and paleoclimate) gradients in 2018. We found that SR, and H' and D diversity indices of overstory trees and understory herbs exhibited a unimodal pattern with increasing latitude and elevation (P<0.05) and negative associations with longitude (P<0.01). Along the climatic gradients, there were U-shaped patterns in SR, and H' and D diversity indices between trees and herbs (P<0.05). SR, and H' and D diversity indices for overstory tree species were positively associated with those for understory herbs (P<0.01). These findings indicate that overstory trees and understory herbs should be protected concurrently in the TWFF to increase effectiveness of species diversity conservation programs.

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Eco-physiological studies on desert plants: germination of Halothamnus iraqensis Botsch. seeds under different conditions
BHATT Arvind, R BHAT Narayana, MURRU Valentina, SANTO Andrea
Journal of Arid Land    2019, 11 (1): 75-85.   DOI: 10.1007/s40333-019-0121-7
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With the aim to investigate if the halophyte HalothamnusiraqensisBotsch.can be suitable for re-vegetation and remediation of salt-affected lands, this study evaluated(1) the effects of photoperiod, thermoperiod, storage period and wings' presenceon its seed germination, and (2) the ability of its seeds to have successful germination recovery after salt stress. Germination tests in different photoperiods (12 hlight/12 h darkness and total darkness) and thermoperiods (15°C/20°C and 20°C/25°C) were conducted for seeds collected in 2012, 2013, 2014, 2015 and2016. The seeds collected in 2016 were sown under different salinity levels(0, 100, 200, 400 and 600 mMNaCl)to assess the salinity tolerance during the germination. Wings' presence highly inhibited seed germination of this species in both photoperiods andthermoperiodsunder all salinity level treatments. In addition, the germination recovery occurred well when seeds were deprived of their wings. The photoperiod of 12 h light/12 h darkness and the thermoperiodof 15°C/20°Cwere the best conditions for seed germination. Germination percentages of H. iraqensis seeds decreased with the increasing storage duration, especially after three years of the collection.In addition, H. iraqensisseeds were able to germinate under different salinity levels, and their germination percentages decreased with increasing salinity levels. H. iraqensisseeds have the ability to recover their germinationafteralleviating the salt stress, irrespective of photoperiod, highlighting the halophilous character of this species.

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Investigation of crop evapotranspiration and irrigation water requirement in the lower Amu Darya River Basin, Central Asia
Durdiev KHAYDAR, CHEN Xi, HUANG Yue, Makhmudov ILKHOM, LIU Tie, Ochege FRIDAY, Abdullaev FARKHOD, Gafforov KHUSEN, Omarakunova GULKAIYR
Journal of Arid Land    2021, 13 (1): 23-39.   DOI: 10.1007/s40333-021-0054-9
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High water consumption and inefficient irrigation management in the agriculture sector of the middle and lower reaches of the Amu Darya River Basin (ADRB) have significantly influenced the gradual shrinking of the Aral Sea and its ecosystem. In this study, we investigated the crop water consumption in the growing seasons and the irrigation water requirement for different crop types in the lower ADRB during 2004-2017. We applied the FAO Penman-Monteith method to estimate reference evapotranspiration (ET0) based on daily climatic data collected from four meteorological stations. Crop evapotranspiration (ETc) of specific crop types was calculated by the crop coefficient. Then, we analyzed the net irrigation requirement (NIR) based on the effective precipitation with crop water requirements. The results indicated that the lowest monthly ET0 values in the lower ADRB were found in December (18.2 mm) and January (16.0 mm), and the highest monthly ET0 values were found in June and July, with similar values of 211.6 mm. The annual ETc reached to 887.2, 1002.1, and 492.0 mm for cotton, rice, and wheat, respectively. The average regional NIR ranged from 514.9 to 715.0 mm in the 10 Irrigation System Management Organizations (UISs) in the study area, while the total required irrigation volume for the whole region ranged from 4.2×109 to 11.6×109 m3 during 2004-2017. The percentages of NIR in SIW (surface irrigation water) ranged from 46.4% to 65.2% during the study period, with the exceptions of the drought years of 2008 and 2011, in which there was a significantly less runoff in the Amu Darya River. This study provides an overview for local water authorities to achieve optimal regional water allocation in the study area.

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Soil fixation and erosion control by Haloxylon persicum roots in arid lands, Iran
ABDI Ehsan, R SALEH Hamid, MAJNONIAN Baris, DELJOUEI Azade
Journal of Arid Land    2019, 11 (1): 86-96.   DOI: 10.1007/s40333-018-0021-2
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Vegetation roots contribute to soil fixation and reinforcement, thus improving soil resistance against erosion. Generally, the amount of soil fixation presented by roots mainly depends on root density and tensile strength. In the present study, we conducted the research in order to further understand the biotechnical properties of Haloxylon persicum and also to quantify its role in increasing soil cohesion in arid lands of Iran. Ten H. persicum shrubs were randomly selected for root distribution and strength investigations, in which five samples were set on flat terrain and other five samples on a moderate slope terrain. The profile trench method was used to assess the root area ratio (RAR) as the index of root density and distribution. Two profiles were dug around each sample, up and downslope for sloped treatment and north and south sides for flat treatment. The results showed that RAR increased with increasing soil depth and significantly decreased in 40-50 cm layers of downhill (0.320%) and 50-60 cm for uphill (0.210%). The minimum values for the northward and southward profiles were 0.003% and 0.003%, respectively, while the maximum values were 0.260% and 0.040%, respectively. The relationship between the diameter of root samples and root tensile strength followed a negative power function, but tensile force increased with increasing root diameter following a positive power function. The pattern of increased cohesion changes in soil profile was relatively similar to RAR curves. The maximum increased cohesion due to the presence of roots in uphill and downhill sides were 0.470 and 1.400 kPa, respectively. In the flat treatment, the maximum increased cohesions were 0.570 and 0.610 kPa in northward and southward profiles, respectively. The analysis of variance showed that wind and slope induced stresses did not have any significant effect on the amount of increased cohesion of H. persicum. The findings served to develop knowledge about biotechnical properties of H. persicum root system that can assist in assessing the efficiency of afforestation and restoration measures for erosion control in arid lands.

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Derivation of salt content in salinized soil from hyperspectral reflectance data: A case study at Minqin Oasis, Northwest China
Tana QIAN, TSUNEKAWA Atsushi, Fei PENG, TsugiyukiMASUNAGA, Tao WANG, Rui LI
Journal of Arid Land    2019, 11 (1): 111-122.   DOI: 10.1007/s40333-019-0091-9
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Soil salinization is a serious ecological and environmental problem because it adversely affects sustainable development worldwide, especially in arid and semi-aridregions. It is crucial and urgent that advanced technologies are used to efficiently and accurately assess the status of salinization processes. Case studies to determine the relations between particular types of salinization and their spectral reflectances are essential because of the distinctive characteristics of the reflectance spectra of particular salts. During April 2015 we collected surface soil samples (0-10 cm depth) at 64 field sites in the downstream area of Minqin Oasis in Northwest China, an area that is undergoing serious salinization. We developed a linear model for determination of salt content in soil from hyperspectral data as follows. First, we undertook chemical analysis of the soil samples to determine their soluble salt contents. We then measured the reflectance spectra of the soil samples, which we post-processed using a continuum-removed reflectance algorithm to enhance the absorption features and better discriminate subtle differences in spectral features. We applied a normalized difference salinity index to the continuum-removed hyperspectral data to obtain all possible waveband pairs. Correlation of the indices obtained for all of the waveband pairs with the wavebands corresponding to measured soil salinities showed that two wavebands centred at wavelengths of 1358 and 2382 nm had the highest sensitivity to salinity. We then applied the linear regression modelling to the data from half of the soil samples to develop a soil salinity index for the relationshipsbetween wavebands and laboratory measured soluble salt content. We used the hyperspectral data from the remaining samples to validate the model. The salt content in soil from Minqin Oasis were well produced by themodel. Our results indicate that wavelengths at 1358 and 2382 nm are the optimal wavebands for monitoring the concentrations of chlorine and sulphate compounds, the predominant salts at Minqin Oasis. Our modelling provides a reference for future case studies on the use of hyperspectral data for predictive quantitative estimation of salt content in soils in arid regions. Further research is warranted on the application of this method to remotely sensed hyperspectral data to investigate its potential use for large-scale mapping of the extent and severity of soil salinity.

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Determining the spatial distribution of soil properties using the environmental covariates and multivariate statistical analysis: a case study in semi-arid regions of Iran
ZERAATPISHEH Mojtaba, AYOUBI Shamsollah, SULIEMAN Magboul, RODRIGO-COMINO Jesús
Journal of Arid Land    2019, 11 (4): 551-566.   DOI: 10.1007/s40333-019-0059-9
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Natural soil-forming factors such as landforms, parent materials or biota lead to high variability in soil properties. However, there is not enough research quantifying which environmental factor(s) can be the most relevant to predicting soil properties at the catchment scale in semi-arid areas. Thus, this research aims to investigate the ability of multivariate statistical analyses to distinguish which soil properties follow a clear spatial pattern conditioned by specific environmental characteristics in a semi-arid region of Iran. To achieve this goal, we digitized parent materials and landforms by recent orthophotography. Also, we extracted ten topographical attributes and five remote sensing variables from a digital elevation model (DEM) and the Landsat Enhanced Thematic Mapper (ETM), respectively. These factors were contrasted for 334 soil samples (depth of 0-30 cm). Cluster analysis and soil maps reveal that Cluster 1 comprises of limestones, massive limestones and mixed deposits of conglomerates with low soil organic carbon (SOC) and clay contents, and Cluster 2 is composed of soils that originated from quaternary and early quaternary parent materials such as terraces, alluvial fans, lake deposits, and marls or conglomerates that register the highest SOC content and the lowest sand and silt contents. Further, it is confirmed that soils with the highest SOC and clay contents are located in wetlands, lagoons, alluvial fans and piedmonts, while soils with the lowest SOC and clay contents are located in dissected alluvial fans, eroded hills, rock outcrops and steep hills. The results of principal component analysis using the remote sensing data and topographical attributes identify five main components, which explain 73.3% of the total variability of soil properties. Environmental factors such as hillslope morphology and all of the remote sensing variables can largely explain SOC variability, but no significant correlation is found for soil texture and calcium carbonate equivalent contents. Therefore, we conclude that SOC can be considered as the best-predicted soil property in semi-arid regions.

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Variation and heritability of morphological and physiological traits among Leymus chinensis genotypes under different environmental conditions
Xue YANG, Junpeng LI, Tingting ZHAO, Lidong MO, Jianli ZHANG, Huiqin REN, Nianxi ZHAO, Yubao GAO
Journal of Arid Land    2019, 11 (1): 66-74.   DOI: 10.1007/s40333-018-0018-x
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Intraspecific trait variation and heritability in different environmental conditions not only suggest a potential for an evolutionary response but also have important ecological consequences at the population, community, and ecosystem levels. However, the contribution of quantitative trait variation within a grassland species to evolutionary responses or ecological consequences is seldom documented. Leymus chinensis is an important dominant species in semi-arid grasslands of China, which has seriously suffered from drought and high temperature stresses in recent decades. In the present study, we measured variation and heritability of 10 quantitative traits, namely the number of tillers, maximum shoot height, number of rhizomes, maximum rhizome length, rhizome mass, aboveground mass, root mass, maximum net photosynthetic rate (Pmax), specific leaf area (SLA), and leaf length to leaf width ratio (LL/LW), for 10 genotypes of L. chinensis under one non-stress (Ck) condition and three environmental stress conditions (i.e., drought (Dr), high temperature (Ht), and both drought and high temperature (DrHt)). Result indicated that (1) the interaction of genotype and environmental condition (G×E) was significant for 6 traits but not significant for the other 4 traits as shown by two-way analysis of variance (ANOVA), suggesting that different selection forces were placed for different traits on the factors dominating phenotypic responses to different environmental conditions. Moreover, these significant G×E effects on traits indicated significantly different phenotypic adaptive responses among L. chinensis genotypes to different environmental conditions. Additionally, individuals could be grouped according to environmental condition rather than genotype as shown by canonical discriminant analysis, indicating that environmental condition played a more important role in affecting phenotypic variation than genotype; (2) by one-way ANOVA, significant differences among L. chinensis genotypes were found in all 10 traits under Ck and Dr conditions, in 8 traits under DrHt condition and only in 4 traits under Ht condition; and (3) all 10 traits showed relatively low or non-measurable broad-sense heritability (H2) under stress conditions. However, the lowest H2 value for most traits did not occur under DrHt condition, which supported the hypothesis of 'unfavorable conditions have unpredictable effects' rather than 'unfavorable conditions decrease heritability'. Results from our experiment might aid to improve predictions on the potential impacts of climate changes on L. chinensis and eventually species conservation and ecosystem restoration.

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Hydrological and water cycle processes of inland river basins in the arid region of Northwest China
Yaning CHEN, Baofu LI, Yuting FAN, Congjian SUN, Gonghuan FANG
Journal of Arid Land    2019, 11 (2): 161-179.   DOI: 10.1007/s40333-019-0050-5
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The increasing shortage in water resources is a key factor affecting sustainable socio-economic development in the arid region of Northwest China (ARNC). Water shortages also affect the stability of the region's oasis ecosystem. This paper summarizes the hydrological processes and water cycle of inland river basins in the ARNC, focusing on the following aspects: the spatial-temporal features of water resources (including air water vapor resources, runoff, and glacial meltwater) and their driving forces; the characteristics of streamflow composition in the inland river basins; the characteristics and main controlling factors of baseflow in the inland rivers; and anticipated future changes in hydrological processes and water resources. The results indicate that: (1) although the runoff in most inland rivers in the ARNC showed a significant increasing trend, both the glaciated area and glacial ice reserves have been reduced in the mountains; (2) snow melt and glacier melt are extremely important hydrological processes in the ARNC, especially in the Kunlun and Tianshan mountains; (3) baseflow in the inland rivers of the ARNC is the result of climate change and human activities, with the main driving factors being the reduction in forest area and the over-exploitation and utilization of groundwater in the river basins; and (4) the contradictions among water resources, ecology and economy will further increase in the future. The findings of this study might also help strengthen the ecological, economic and social sustainable development in the study region.

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Global Dryland Ecosystem Programme (G-DEP): Africa consultative meeting report
PENG Yu, FU Bojie, ZHANG Linxiu, YU Xiubo, FU Chao, Salif DIOP, Hubert HIRWA, Aliou GUISSE, LI Fadong
Journal of Arid Land    2020, 12 (3): 538-544.   DOI: 10.1007/s40333-020-0056-z
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In order to enhance and restore the ecosystems of natural capital in African arid regions, the Global Dryland Ecosystem Programme (G-DEP) consultative meeting was hosted in Dakar, Senegal, from 23 to 25 September 2019. This paper details the first African meeting of the G-DEP. Consultative meeting reviewed preceding dryland ecosystems case studies, identified vulnerable arid and semi-arid regions, and proposed sustainable solutions to problems. It also identified the successes and failures of previous attempts to improve vulnerable ecosystems and ultimately formed an action plan to improve these attempts. Climate, ecosystems, and livelihoods for Sustainable Development Goals (SDGs), Great Green Wall Initiative (GGWI) for Sahara and Sahel, and China-Africa cooperation on science, technology, and innovation are three extra main sections concerned of the meeting. Separately, more specific topics as the complicated relationship between these natural processes and human activity, including pastoralism, soil restoration, and vegetation regenerate techniques, were fully discussed. Consultative meeting also identified the positive effects international collaboration can have on dryland regions, specifically in the capacity of sharing information, technology, and innovation on purpose to develop a joint proposal for long-term research programs in African arid and semi-arid areas. Moreover, meetings that review the progress made on ecosystem management for the sustainable livelihoods in Africa, identification of priority areas, and the development and implementation of ecosystem programs for proper research and collaboration in African arid and semi-arid zones, have been proposed as strategic recommendations to enhance the global partnership for sustainable development. Furthermore, as the outcomes of the workshop, there are three steps proposed to handle African dryland climate changes, several aspects suggested to solve current dilemmas of the GGWI, and a series of actions recommended for G-DEP related activities in Africa.

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Spatio-temporal dynamics of vegetation in Jungar Banner of China during 2000-2017
LI Xinhui, LEI Shaogang, CHENG Wei, LIU Feng, WANG Weizhong
Journal of Arid Land    2019, 11 (6): 837-854.   DOI: 10.1007/s40333-019-0067-9
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It is known that the exploitation of opencast coal mines has seriously damaged the environments in the semi-arid areas. Vegetation status can reliably reflect the ecological degeneration and restoration in the opencast mining areas in the semi-arid areas. Long-time series MODIS NDVI data are widely used to simulate the vegetation cover to reflect the disturbance and restoration of local ecosystems. In this study, both qualitative (linear regression method and coefficient of variation (CoV)) and quantitative (spatial buffer analysis, and change amplitude and the rate of change in the average NDVI) analyses were conducted to analyze the spatio-temporal dynamics of vegetation during 2000-2017 in Jungar Banner of Inner Mongolia Autonomous Region, China, at the large (Jungar Banner and three mine groups) and small (three types of functional areas: opencast coal mining excavation areas, reclamation areas and natural areas) scales. The results show that the rates of change in the average NDVI in the reclamation areas (20%-60%) and opencast coal mining excavation areas (10%-20%) were considerably higher than that in the natural areas (<7%). The vegetation in the reclamation areas experienced a trend of increase (3-5 a after reclamation)-decrease (the sixth year of reclamation)-stability. The vegetation in Jungar Banner has a spatial heterogeneity under the influences of mining and reclamation activities. The ratio of vegetation improvement area to vegetation degradation area in the west, southwest and east mine groups during 2000-2017 was 8:1, 20:1 and 33:1, respectively. The regions with the high CoV of NDVI above 0.45 were mainly distributed around the opencast coal mining excavation areas, and the regions with the CoV of NDVI above 0.25 were mostly located in areas with low (28.8%) and medium-low (10.2%) vegetation cover. The average disturbance distances of mining activities on vegetation in the three mine groups (west, southwest and east) were 800, 800 and 1000 m, respectively. The greater the scale of mining, the farther the disturbance distances of mining activities on vegetation. We conclude that vegetation reclamation will certainly compensate for the negative impacts of opencast coal mining activities on vegetation. Sufficient attention should be paid to the proportional allocation of plant species (herbs and shrubs) in the reclamation areas, and the restored vegetation in these areas needs to be protected for more than 6 a. Then, as the repair time increased, the vegetation condition of the reclamation areas would exceed that of the natural areas.

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Assessment of drought hazard, vulnerability and risk in Iran using GIS techniques
Esmail HEYDARI ALAMDARLOO, Hassan KHOSRAVI, Sahar NASABPOUR, Ahmad GHOLAMI
Journal of Arid Land    2020, 12 (6): 984-1000.   DOI: 10.1007/s40333-020-0096-4
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The drought has enormous adverse effects on agriculture, water resources and environment, and causes damages around the world. Drought risk assessment and prioritization of drought management can help decision makers and planners to manage the adverse effects of drought. This paper aims to determine the risk of drought in Iran. At the first stage, standardized precipitation index (SPI) was calculated for the period 1981-2016. Then the probability map of different drought classes or drought hazard probability map were prepared. After that the indicator-based vulnerability assessment method was used to determine the drought vulnerability index. Five indices including climate, topography, waterway density, land use and groundwater resources were chosen as the most critical factors of drought in Iran and followed by the analytical hierarchy process questionnaire, the weights of each index were obtained based on expert opinions. Fuzzy membership maps of each index and sub-index were prepared using ArcGIS software. The drought vulnerability map of Iran was plotted using these weights and maps of each indicator. Finally, the drought risk map of Iran was provided by multiplying drought hazard and vulnerability maps. According to the 43-completed questionnaires by experts, climate index has the highest vulnerability to drought. Climate does not have an important role in drought hazard index, but it is the most crucial factor to classified drought vulnerability index. The results showed that central, northeast, southeast and west parts of Iran are at high risks of drought. There are regions with different risks in Iran due to unusual weather and climatic conditions. We realized that the climate and the groundwater situation is almost the same in the central, east and south parts of Iran, because the land use plays a crucial role in the drought vulnerability and risk in these areas. The drought risk decreases from the center of Iran to the southwest and northwest.

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Comparison of two remote sensing models for estimating evapotranspiration: algorithm evaluation and application in seasonally arid ecosystems in South Africa
DZIKITI Sebinasi, Z JOVANOVIC Nebo, DH BUGAN Richard, RAMOELO Abel, P MAJOZI Nobuhle, NICKLESS Alecia, A CHO Moses, C LE MAITRE David, NTSHIDI Zanele, H PIENAAR Harrison
Journal of Arid Land    2019, 11 (4): 495-512.   DOI: 10.1007/s40333-019-0098-2
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Remote sensing tools are becoming increasingly important for providing spatial information on water use by different ecosystems. Despite significant advances in remote sensing based evapotranspiration (ET) models in recent years, important information gaps still exist on the accuracy of the models particularly in arid and semi-arid environments. In this study, we evaluated the Penman-Monteith based MOD16 and the modified Priestley-Taylor (PT-JPL) models at the daily time step against three measured ET datasets. We used data from two summer and one winter rainfall sites in South Africa. One site was dominated by native broad leaf and the other by fine leafed deciduous savanna tree species and C4 grasses. The third site was in the winter rainfall Cape region and had shrubby fynbos vegetation. Actual ET was measured using open-path eddy covariance systems at the summer rainfall sites while a surface energy balance system utilizing the large aperture boundary layer scintillometer was used in the Cape. Model performance varied between sites and between years with the worst estimates (R2<0.50 and RMSE>0.80 mm/d) observed during years with prolonged mid-summer dry spells in the summer rainfall areas. Sensitivity tests on MOD16 showed that the leaf area index, surface conductance and radiation budget parameters had the largest effect on simulated ET. MOD16 ET predictions were improved by: (1) reformulating the emissivity expressions in the net radiation equation; (2) incorporating representative surface conductance values; and (3) including a soil moisture stress function in the transpiration sub-model. Implementing these changes increased the accuracy of MOD16 daily ET predictions at all sites. However, similar adjustments to the PT-JPL model yielded minimal improvements. We conclude that the MOD16 ET model has the potential to accurately predict water use in arid environments provided soil water stress and accurate biome-specific parameters are incorporated.

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Distribution of soil aggregates and organic carbon in deep soil under long-term conservation tillage with residual retention in dryland
Bisheng WANG, Lili GAO, Weishui YU, Xueqin WEI, Jing LI, Shengping LI, Xiaojun SONG, Guopeng LIANG, Dianxiong CAI, Xueping WU
Journal of Arid Land    2019, 11 (2): 241-254.   DOI: 10.1007/s40333-019-0094-6
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To ascertain the effects of long-term conservation tillage and residue retention on soil organic carbon (SOC) content and aggregate distribution in a deep soil (>20-cm depth) in a dryland environment, this paper analyzed the SOC and aggregate distribution in soil, and the aggregate-associated organic carbon (OC) and SOC physical fractions. Conservation tillage (reduced tillage with residue incorporated (RT) and no-tillage with residue mulch (NT)) significantly increased SOC sequestration and soil aggregation in deep soil compared with conventional tillage with residue removal (CT). Compared with CT, RT significantly increased the proportion of small macroaggregates by 23%-81% in the 10-80 cm layer, and the OC content in small macroaggregates by 1%-58% in the 0-80 cm layer. RT significantly increased (by 24%-90%) the OC content in mineral-SOC within small macroaggregates in the 0-60 cm layer, while there was a 23%-80% increase in the 0-40 cm layer with NT. These results indicated that: (1) conservation tillage treatments are beneficial for soil aggregation and SOC sequestration in a deep soil in a dryland environment; and (2) the SOC in mineral-associated OC plays important roles in soil aggregation and SOC sequestration. In conclusion, RT with NT is recommended as an agricultural management tool in dryland soils because of its role in improving soil aggregation and SOC sequestration.

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Abrupt temperature change and a warming hiatus from 1951 to 2014 in Inner Mongolia, China
Long MA, Hongyu LI, Tingxi LIU, Longteng LIANG
Journal of Arid Land    2019, 11 (2): 192-207.   DOI: 10.1007/s40333-019-0100-z
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An abrupt temperature change and a warming hiatus have strongly influenced the global climate. This study focused on these changes in Inner Mongolia, China. This study used the central clustering method, Mann-Kendall mutation test and other methods to explore the abrupt temperature change and warming hiatus in three different temperature zones of the study region based on average annual data series. Among the temperature metrics investigated, average minimum temperature (Tnav) shifted the earliest, followed by average temperature (Tnv) and average maximum temperature (Txav). The latest change was observed in summer (1990s), whereas the earliest was observed in winter (1970s). Before and after the abrupt temperature change, Tnavfluctuatedconsiderably, whereas there was only a slight change in Txav. Before and after the abrupt temperature change, the winter temperature changed more dramatically than the summer temperature. Before the abrupt temperature change, Tnav in the central region (0.322°C/10a) and west region (0.48°C/10a) contributed the most to the increasing temperatures. After the abrupt temperature change, Tnav in winter in the central region (0.519°C/10a) and in autumn in the west region (0.729°C/10a) contributed the most to the temperature increases. Overall, in the years in which temperature shifts occurred early, a warming hiatus also appeared early. The three temperature metrics in spring (1991) in the east region were the first to exhibit a warming hiatus. In the east region, Txav displayed the lowest rate of increase (0.412°C/a) in the period after the abrupt temperature change and before the warming hiatus, and the highest rate of increase after the warming hiatus.

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Low-carbon economic development in Central Asia based on LMDI decomposition and comparative decoupling analyses
Jiaxiu LI, Yaning CHEN, Zhi LI, Xiaotao HUANG
Journal of Arid Land    2019, 11 (4): 513-524.   DOI: 10.1007/s40333-019-0063-0
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Low-carbon economic development is a strategy that is emerging in response to global climate change. Being the third-largest energy base in the world, Central Asia should adopt rational and efficient energy utilization to achieve the sustainable economic development. In this study, the logarithmic mean Divisia index (LMDI) decomposition method was used to explore the influence factors of CO2 emissions in Central Asia (including Kazakhstan, Uzbekistan, Kyrgyzstan, Tajikistan and Turkmenistan) during the period 1992-2014. Moreover, decoupling elasticity and decoupling index based on the LMDI decomposition results were employed to explore the relationship between economic growth and CO2 emissions during the study period. Our results show that the total CO2 emissions decreased during the period 1992-1998, influenced by the collapse of the Soviet Union in 1991 and the subsequent financial crisis. After 1998, the total CO2 emissions started to increase slowly along with the economic growth after the market economic reform. Energy-related CO2 emissions increased in Central Asia, mainly driven by economic activity effect and population effect, while energy intensity effect and energy carbon structure effect were the primary factors inhibiting CO2 emissions. The contribution percentages of these four factors (economic activity effect, population effect, energy intensity effect and energy carbon structure effect) to the total CO2 emissions were 11.80%, 39.08%, -44.82% and -4.32%, respectively, during the study period. Kazakhstan, Uzbekistan and Turkmenistan released great quantities of CO2 with the annual average emissions of 189.69×106, 45.55×106 and 115.38×106 t, respectively. In fact, their economic developments depended on high-carbon energies. The decoupling indices clarified the relationship between CO2 emissions and economic growth, highlighting the occurrence of a ''weak decoupling'' between these two variables in Central Asia. In conclusion, our results indicate that CO2 emissions are still not completely decoupled from economic growth in Central Asia. Based on these results, we suggest four key policy suggestions in this paper to help Central Asia to reduce CO2 emissions and build a resource-conserving and environment-friendly society.

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Mesophyll thickness and sclerophylly among Calotropis procera morphotypes reveal water-saved adaptation to environments
Marcelo F POMPELLI, Keila R MENDES, Marcio V RAMOS, José N B SANTOS, Diaa T A YOUSSEF, Jaqueline D PEREIRA, Laurício ENDRES, Alfredo JARMA-OROZCO, Rodolfo SOLANO-GOMES, Betty JARMA-ARROYO, André L J SILVA, Marcos A SANTOS, Werner C ANTUNES
Journal of Arid Land    2019, 11 (6): 795-810.   DOI: 10.1007/s40333-019-0016-7
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Calotropis procera (Aiton) Dryand (Apocynaceae) is a native species in tropical and subtropical Africa and Asia. However, due to its fast growing and drought-tolerant, it has become an invasive species when it was introduced into Central and South America, as well as the Caribbean Islands. Currently, C. procera displays a wide distribution in the world. Invasiveness is important, in particular, because many invasive species exert a high reproductive pressure on the invaded communities or are highly productive in their new distributed areas. It has been suggested that a very deep root system and a high capacity to reduce stomatal conductance during water shortage could allow this species to maintain the water status required for a normal function. However, the true mechanism behind the successful distribution of C. procera across wet and dry environments is still unknown. C. procera leaves were collected from 12 natural populations in Brazil, Colombia and Mexico, ranging from wet to dry environments during 2014-2015. Many traits of morphology and anatomy from these distinct morphotypes were evaluated. We found that C. procera leaves had a considerable capacity to adjust their morphological, anatomical and physiological traits to different environments. The magnitude of acclimation responses, i.e., plasticity, had been hypothesized to reflect the specialized adaptation of plant species to a particular environment. However, allometric models for leaf area (LA) estimation cannot be grouped as a single model. Leaves are narrower and thicker with low amounts of air spaces inside the leaf parenchyma in wet environments, while they are broader and thinner with a small number of palisade cell layers in dry environments. Based on these, we argue that broader and thinner leaves of C. procera dissipate incident energy at the expense of a higher rate of transpiration to survive in environments in which water is the most limiting factor and to compete in favorable wet environments.

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Assessing land transformation and associated degradation of the west part of Ganga River Basin using forest cover land use mapping and residual trend analysis
MATIN Shafique, GHOSH Sujit, D BEHERA Mukunda
Journal of Arid Land    2019, 11 (1): 29-42.   DOI: 10.1007/s40333-018-0106-y
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The west part of Ganga River Basin (WGRB) has experienced continuous land transformation since the Indus Valley Civilisation shifted from the Indus basin to the Ganga basin. Particularly in the last few decades the land transformation has increased many-folds due to the changing climate and rapid increase in population. In this paper, we assessed land transformation and associated degradation in the WGRB based on the forest cover land use (FCLU) mapping and residual trend analysis (RTA). The FCLU maps for 1975 and 2010 were generated using 216 Landsat satellite images and validated using 1509 ground points. We mapped 29 forest and 18 non-forest types and estimated a total loss of 5571 km2 forest cover and expansion in settlement areas (5396 km2). Other major changes mapped include a decrease in wetlands and water bodies, while an increase in agriculture and barren lands with an overall mapping accuracy of 85.3% (kappa, 0.82) and 88.43% (kappa, 0.84) for 1975 and 2010, respectively. We also performed the RTA analysis using GIMMS-NDVI3g to identify areas of significant negative vegetative photosynthetic change as an indicator for land degradation. All the RTA models showed monotonic nature of the residual trends and resulted as moderately positive but highly significant (P<0.001). Land degradation in the form of barren land accompanied by a decline in vegetation quality and coverage was found prominent in the basin with a possibility of an accelerated rate of land degradation in future due to the rapid loss of permanent forest cover.

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Spatial variability of soil water content and related factors across the Hexi Corridor of China
Xiangdong LI, Ming'an SHAO, Chunlei ZHAO, Xiaoxu JIA
Journal of Arid Land    2019, 11 (1): 123-134.   DOI: 10.1007/s40333-018-0123-x
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Soil water content (SWC) is a key factor limiting ecosystem sustainability in arid and semi-arid areas of the Hexi Corridor of China, which is characterized by an ecological environment that is vulnerable to climate change. However, there is a knowledge gap regarding the large-scale spatial distribution of SWC in this region. The specific objectives of this study were to determine the spatial distribution patterns of SWC across the Hexi Corridor and identify the factors responsible for spatial variation of SWC at a regional scale. This study collected and analyzed SWC in the 0-100 cm soil profile from 109 field sampling sites (farmland, grassland and forestland) across the Hexi Corridor in 2017. We selected 17 factors, including land use, topography (latitude, longitude, elevation, slope gradient, and slope aspect), soil properties (soil clay content, soil silt content, soil bulk density, saturated hydraulic conductivity, field capacity, and soil organic carbon content), climate factors (mean annual precipitation, potential evaporation, and aridity index), plant characteristic (vegetation coverage) and planting pattern (irrigation or rain-fed), as possible environmental variables to analyze their effects on SWC. The results showed that SWC was 0.083 (±0.067) g/g in the 0-100 cm soil profile and decreased in the order of farmland, grassland and forestland. The SWC in the upper soil layers (0-20, 20-40 and 40-60 cm) had obvious difference when the mean annual precipitation differed by 200 mm. The SWC decreased from southeast to northwest following the same pattern as precipitation, and had a moderate to strong spatial dependence in a large effective range (75-378 km). The SWC showed a similar distribution and had no significant difference between soil layers in the 0-100 cm soil profile. The principal component analysis showed that the mean annual precipitation, geographical position (longitude and latitude) and soil properties (soil bulk density and soil clay content) were the main factors dominating the variance of environmental variables. A stepwise linear regression equation showed that plant characteristic (vegetation coverage) and soil properties (soil organic carbon content, field capacity and soil clay content) were the optimal factors to predict the variation of SWC. Soil clay content could be better to explain the SWC variation in the deeper soil layers compared with the other factors.

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Spatial distribution of water-activesoil layer along the south-north transect in the Loess Plateau of China
Chunlei ZHAO, Ming'an SHAO, Xiaoxu JIA, Laiming HUANG, Yuanjun ZHU
Journal of Arid Land    2019, 11 (2): 228-240.   DOI: 10.1007/s40333-019-0051-4
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Soil water is an important compositionof water recyclein the soil-plant-atmosphere continuum. However, intense water exchange between soil-plant and soil-atmosphereinterfacesonly occurs in a certain layer of the soil profile. For deep insight into wateractive layer (WAL, defined as the soil layer with a coefficient of variation in soil water content>10% in a given time domain)inthe Loess Plateau of China,we measuredsoil water content (SWC)in the 0.0-5.0 m soil profile from 86 sampling sites along an approximately 860-kmlong south-north transect during the period 2013-2016. Moreover, a datasetcontainedfourclimatic factors (mean annual precipitation, mean annual evaporation, annual mean temperature and mean annual dryness index) andfivelocalfactors (altitude, slope gradient, land use, clay content and soil organic carbon)ofeachsampling sitewasobtained.Inthisstudy, three WAL indices (WAL-T (the thickness of WAL), WAL-CV (the mean coefficient of variation in SWC within WAL) and WAL-SWC (themean SWC within WAL)) were used to evaluate the characteristics of WAL. The results showed that with increasing latitude, WAL-T and WAL-CV increased firstly and then decreased. WAL-SWC showed an oppositedistribution pattern along the south-north transect compared with WAL-T and WAL-CV. Average WAL-T of the transect was 2.0 m, suggesting intense soil water exchange in the0.0-2.0 m soil layer in the study area. Soil water exchange was deeper and more intense in the middle region than in the southern and northern regions, with the values of WAL-CV and WAL-Tbeing27.3% and 4.3 m in the middle region, respectively. Both climatic (10.1%) and local (4.9%) factors influenced the indices of WAL, with climatic factors having a more dominant effect.Compared with multiple linear regressions, pedotransfer functions (PTFs) from artificial neural network can better estimate theWAL indices. PTFs developed byartificial neural network respectivelyexplained 86%, 81% and 64% of the total variations in WAL-T, WAL-SWC andWAL-CV. Knowledge of WAL iscrucial for understanding the regional water budgetandevaluatingthe stable soil water reserve, regional water characteristics and eco-hydrological processes in the Loess Plateau of China.

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